STAR Physics @ RNC

X. DongNov. 27th, 2012 Director’s Review

STAR Physics @ RNC

Xin DongNuclear Science Division / LBNL

1) QCD in cold nuclear matter

2) QCD in hot nuclear matter

• sQGP properties

• QCD phase structure

3) QCD in nucleon spin structure

STAR

Physics

Program

X. DongNov. 27th, 2012 Director’s Review

Relativistic Heavy Ion Collider

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Heavy Ion Collisions: Au + Au √sNN = 7.7, 11.5, 19.6, 27, 39, 62.4, 130, 200 GeV Cu + Cu = 22.4, 62.4, 200 GeV

d + Au = 200 GeV U + U 193 GeV, Cu + Au 200 GeV

Polarized p + p Collisions: √s = 62.4, 200, 500 GeV

€

rp +

r p

€

p↑ + p↑

STAR

X. DongNov. 27th, 2012 Director’s Review

STAR Detector

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• Large & uniform acceptance at mid-rapidity (exploring forward upgrades)• Excellent particle identification• Fast data acquisition

X. DongNov. 27th, 2012 Director’s Review

RHIC Discoveries

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ST

AR

: PR

L. 99 (2007) 112301

Formation of strongly-coupled Quark Gluon Plasma (sQGP)!

v2

ST

AR

: PR

L. 91 (2003) 072304

“Jet Quenching”

- Significant suppression in particle yield at high pT in central heavy ion collisions

“Partonic Collectivity”

- Strong collective flow, even for multi-strange hadrons (, )- Flow driven by Number-of-Constituent-Quark (NCQ) in hadrons

Two most significant discoveries originated in RNC:

X. DongNov. 27th, 2012 Director’s Review

HI Physics Focus of RNC

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1) Study sQGP Properties

• Systematic investigation of partonic collectivity

– Identified particle v2

• Chiral properties / thermal radiation

– Dielectron production (energy dependence)

• Thermalization

– Heavy Quark Production (D-meson, J/)

• Partonic energy loss

– Jets, high pT correlations

2) Study QCD phase structure - Beam Energy Scan

• Turn-off of sQGP signatures

– elliptic flow of identified particles

– Rcp of charged hadrons

• Search for critical point

– high moments of net-proton multiplicity

X. DongNov. 27th, 2012 Director’s Review

Partonic Collectivity

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H. Masui, Md. Nasim (Oct. – Dec. 2011)

STAR, QM 2012

Precision measurements of identified particle v2

- push the limits of partonic collectivity - provide constraints to study the sQGP properties

• 0-30%: baryon-meson grouping / NCQ scaling holds. • 30-80%: Multi-strange hadron v2 deviate from NCQ scaling at mT-m0>1 GeV/c2. v2()<v2(Ks), v2()<v2()

X. DongNov. 27th, 2012 Director’s Review

Charm production cross section

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X.D., Y. Zhang (now at USTC)

STAR, QM 2011, QM 2012STAR, PRD 86 (2012) 072013

• Heavy quarks – Sensitive to degree of thermalization of early system.

• consistent with the pQCD calculation in p+p.

• predominantly created from initial hard scatterings in HI collisions.

pQCD

X. DongNov. 27th, 2012 Director’s Review8

Open Charm Hadrons in Au+Au collisions

• Modification in low pT - indication of strong charm-medium interactions.

• Large suppression at high pT - indication of large energy loss in the sQGP.

• Future precision measurements with HFT: RAA, v2, correlations.

Model curves:

He, et al. arX

iv: 1204.4442G

ossiaux, et al. arXiv: 1207.5445

Y. Zhang (now at USTC)

STAR, QM2012

X. DongNov. 27th, 2012 Director’s Review

J/ Production

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STAR, QM2012 C. Powell

• Quarkonium production – color screening in sQGP.

• consistent with a shadowing model + cold nuclear absorption in d+Au.

• J/ freeze-out differently compared to light hadrons- Small (or zero) radial flow- Other production mechanisms (e.g. regeneration)

X. DongNov. 27th, 2012 Director’s Review

J/ v2 – Probe Charm Collectivity

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Au+Au 200 GeV 0-80%

• Disfavor regeneration from thermalized charm quarks at pT > 2 GeV/c.

H. QiuPaper in Collaboration reviewTo be submitted to PRL soon.

STAR, QM2011

X. DongNov. 27th, 2012 Director’s Review

Dielectrons at Au+Au 200 GeV

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• Clean penetrating probe to study various stage of HI collisions

• Goals:o In-medium vector mesons

o Thermal radiation

• Enhancement at 0.3-0.7 GeV/c2 compared to the hadron cocktail.

• Vacuum cannot reproduce the excess observed in data.

- in-medium modification

STAR, QM2011 J. Zhao

X. DongNov. 27th, 2012 Director’s Review

Energy Dependent Dielectron Production

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• Low mass region (LMR) enhancement persists from 19.6 – 200 GeV.

• In-medium broadening reproduce LMR excesses consistently.- Suggestive of (partial) chiral symmetry restoration.

• Future measurements to quantify the correlated charm contribution. - QGP thermal radiation: Cross section, RAA, v2, (M, pT)

In-medium broadening: R. Rapp, private communications

P. HuckSTAR, QM2012

X. DongNov. 27th, 2012 Director’s Review

Beam Energy Scan

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0) Turn-off of sQGP signatures

1)Search for the phase boundary 2) Search for the critical point

BES Phase-I

RNC initiated and is now leading the BES program at RHIC

NSAC Long Range Plan 2007

X. DongNov. 27th, 2012 Director’s Review

Inclusive Charged Hadron v2

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STAR, PRC 86 (2012) 054908 H. Masui, A. Schmah

• Similar v2 behavior over a wide energy range from 7.7 GeV – 2.76 TeV.

v2

Rat

io

X. DongNov. 27th, 2012 Director’s Review

Identified Particle v2

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• Significant difference between baryon-antibaryon v2 at lower energies.• No clear baryon/meson grouping for anti-particles at <=11.5 GeV.

NCQ scaling between particles and anti-particles is broken!

Hadronic interactions play a significant role at √sNN<= 11.5 GeV.

STAR Preliminary

A. Schmah Papers well advanced in the collaboration, to be released soon.

STAR, QM 2012

X. DongNov. 27th, 2012 Director’s Review

Rcp of Charged Hadrons

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jet-quenching off

STAR, QM 2012 E. Sangaline

€

RCP =dN /dpT /Nbin( )

0−5%

dN /dpT /Nbin( )60−80%

• Significant change in the charged hadron Rcp at low energies.

• Similar behavior in HIJING with no partonic energy loss at low energies.- suppression at 200 GeV – partonic energy loss

Hadronic interactions play a significant role at √sNN<= 11.5 GeV.

X. DongNov. 27th, 2012 Director’s Review

Higher Moments of Net-protons

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• Higher moments - more sensitive to Critical Point induced fluctuations.

• A non-monotonic behavior could be indicative of the QCD critical point. • Deviation from Poisson expectation. - can be due to other correlation sources

• Current precision cannot allow a firm conclusion on the energy dependence. • Future precision measurements at low energies.

X.F. Luo (now at CCNU), H.G. Ritter

STAR QM 2012varianceskewness

kurtosis

STAR, PRL 105 (2010) 022302

X. DongNov. 27th, 2012 Director’s Review

Spin Physics at STAR

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€

Sz =1

2=

1

2Δu + Δd + Δs( ) + ΔG + Lz q,g

RNC focus

• Gluon polarization

– Jet double spin asymmetry

• Strange quark polarization

– Hyperon () longitudinal spin transfer

• Transverse spin

– Forward single spin asymmetries (0, )

Nucleon spin structure

25-30% of total spin

X. DongNov. 27th, 2012 Director’s Review19

Gluon Polarization – Jet Asymmetries

• Non-zero gluon polarization for gluon light-cone momenta at the level of 5-20% of the proton momentum and at hard scales.

STARPRL 97 (2006) 252001, PRL 98 (2008) 232003 PRD 86 (2012) 032006, SPIN 2012

2006 data

2009 data

DSSV: Florian et al, PRL 101 (2008) 072001

X. DongNov. 27th, 2012 Director’s Review20

Longitudinal Hyperon Spin Transfer

STAR, SPIN 2012, DNP 2012

Non-relativistic naive quark model, all quarks contribute equally to DLL,

Non-relativistic naive quark model, only strange quarks contribute DLL,

Deep-Inelastic-Scattering like contributions to DLL.

R. Cendejas (now at Penn. State. Univ.)E. Sichtermann

• New sensitivity to s (s) and polarized fragmentation.

• Unique at RHIC and complementary to deep-inelastic lepton-nucleon scattering.

X. DongNov. 27th, 2012 Director’s Review21

Transverse Asymmetries: ,

• AN of , – QCD origin of large asymmetries, OAM contribution in nucleon spin.

• NLO pQCD describes the η production cross section at forward rapidity.

• AN of η might be larger than π0 AN.

STAR, PRD 86 (2012) 051101(R) L. Eun

X. DongNov. 27th, 2012 Director’s Review

Synergies with Theory Group

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• Jet quenching and partonic energy loss

• Hydrodynamic flow

• Correlation / fluctuation

• Heavy flavor

• Dileptons

• Spin

STAR, PRL 91 (2003) 172302

Song, PRL 106 (2011) 192301

Steinheimer, arXiv: 1207.2791

STAR, PRD 86 (2012) 072013

Yuan, PRD 84 (2011) 034019

X. DongNov. 27th, 2012 Director’s Review

STAR Physics Focus in Future

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2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

BES-I

HFT/MTD: Heavy Flavor / Dileptons

BES-II (√sNN ≤ 20GeV)

pA/eA program

Precision measurements on HF and dileptons:Quantify the sQGP properties (hot QCD)

Precision measurements on focused energiesMap out the QCD phase structure

Precision measurements on pA and eAStudy QCD in cold matter

X. DongNov. 27th, 2012 Director’s Review

Future STAR Physics Focus @ RNC

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1) Heavy quark production:

a) Heavy quark collectivity:

- the degree of thermalization

b) Heavy quark RAA and correlations:

- parton energy loss mechanism / medium properties

2) Di-lepton production: cross section, RAA, v2, (M, pT)

3) Full jet reconstruction in heavy ion collisions

4) In preparation of BES-II

5) pA/eA program

– nPDF / evolution from cold nuclear matter to sQGP

X. DongNov. 27th, 2012 Director’s Review25

X. DongNov. 27th, 2012 Director’s Review

High Energy Nucleus-Nucleus Collisions

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Time

Initial hardscatterings

Partonic stage

Hadronicstage

Freeze-out

Nuclear modification factor (RAA)

€

RAA =d2N AA /dpT dy

Nbind2N pp /dpT dy

Characterize the medium effect

Elliptic flow (v2) = 2nd Fourier coefficient

Sensitive to the early stage properties

Observables

X. DongNov. 27th, 2012 Director’s Review27

Future: Thermal Radiation via Di-electrons

Transverse momentum spectra slopes: to disentangle charm and QGP radiation - Au+Au result seems to be higher than p+p and PYTHIA charm at ~ 2 GeV. Suggestive of either charm modifications or other sources.

- Future measurements to quantify the correlated charm contribution. -– QGP thermal radiation: Cross section, RAA, v2, (M, pT)

J. ZhaoSTAR, QM2011

X. DongNov. 27th, 2012 Director’s Review

Future Upgrades

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Near term 2013-TPC

SSD

ISTPXL

1) Heavy Flavor Tracker (HFT) RNC leading the Pixel subproject see Jim Thomas’s talk next

2) Muon Telescope Detector (MTD)

Mid term 2017-

Subsystem upgrade at forward rapidity expanding pA/eA physics program